Thermoplastic polyamides are well-known to have a variety of outstanding properties including resistance to oils and greases, resistance to solvents and bases, fatigue resistance, abrasion resistance, a low coefficient of friction, high tensile strength, and retention of properties over a wide temperature range. However, the impact strength of unmodified polyamides is unsatisfactory for certain applications such as, for example, instrument and tool housings, and for automotive body components.
Plasticizers which have been used to increase impact strength and improve flexibility have associated therewith various well-known disadvantages and are not suitable for imparting good impact strength without dramatically sacrificing rigidity.
U.S. Pat. No. 4,167,505 to Dunkelberger, U.S. Pat. No. 4,495,324 to Chacko et al., and U.S. Pat. No. 4,502,228 to Chen et al. each teach the use of multiphase core/shell type polymer compositions for improving impact resistance. Multiphase core/shell polymers are generally prepared by a relatively complicated and expensive sequential emulsion polymerization process; and, like conventional plasticizers, do not address the problem of providing an impact-modified polyamide which retains a relatively high flexural modulus.
U.S. Pat. No. 4,423,186 to Grigo et al. and U.S. Pat. No. 4,713,415 to Lavengood et al. each teach the use of relatively complicated and expensive polyamide impact modifiers consisting of a copolymer grafted to a diene rubber substrate.
U.S. Pat. No. 4,661,563 to Sasaki et al. and U.S. Pat. No. 4,996,264 to Aonuma et al. each relate to polyamide compositions exhibiting improved impact strength and flexibility. Each of the patents teaches a polyamide composition containing a relatively complicated multiple component impact modifier comprising a crosslinked nitrile rubber, and a crosslinked acrylic rubber or epichlorohydrin rubber. These impact modifiers are intended to also provide for polyamide compositions having increased flexibility and, therefore, do not solve the problem of providing an impact modified polyamide which retains a relatively high flexural modulus.
U.S. Pat. No. 4,321,336 to Meyer et al. and U.S. Pat. No. 4,554,320 to Reimann et al. each relate to polyamide compositions containing a rubbery additive which increases impact resistance and flexibility. Reimann et al. disclose an impact modifier which is a non-crosslinked copolymer having at least 55 percent by weight of ethylene, one or more alkyl acrylates or methacrylates, and at least one monomer possessing an acidic functional group or latent acidic functional group. Meyer et al. disclose an impact modifier which is an aliphatic polyolefin, a copolymer comprising at least 65 percent by weight of an aliphatic monoolefin and a (meth) acrylic acid or ester, a styrene-(meth)acrylic acid-(meth)acrylic ester terpolymer, a diene-acrylonitrile copolymer, or a high molecular weight organic silicon compound. Neither Reimann et al. nor Meyer et al. address the problem of providing an impact modified polyamide composition which retains a relatively high flexural modulus.